Liquid heating system



July 14, 1970 R. T. PFLUGER ET AL 3,520,474

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LIQUID HEATING SYSTEM Filed 001;. 28, 1968 2 Sheets-Sheet 2 III III:

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TTOQME YJ United States Patent Office US. Cl. 237-64 7 Claims ABSTRACT OF THE DISCLOSURE Liquid heated in a boiler by a burner is forced into a conduit and through a radiator by the vapor pressure generated in the boiler and then is delivered to a storage reservoir. After the liquid in the boiler has dropped to a predetermined level and as the burner continues to heat the liquid, a supply of relatively cool liquid is dumped into the boiler from an accumulator tank to cool and condense the vapor in the boiler and to create a vacuum therein for returning the liquid reversely through the conduit from the reservoir and back into the boiler through the tank. The returning liquid which remains after refilling of the boiler is used to refill the tank to create another supply of relatively cool liquid for dumping into the boiler during the next operating cycle.

BACKGROUND OF THE INVENTION This invention relates to a heating system of the type in which liquid is heated in a boiler, is circulated through at least one heat exchanger, and then is returned to the boiler for reheating. More particularly, the invention relates to a so-called single pipe heating system wherein the circulation of the liquid between the boiler and the heat exchanger is dependent neither upon electrical pumps nor gravitational flow and is achieved for the most part through the medium of a single conduit leading from the boiler to the heat exchanger. Such a system is disclosed in Pfluger Pat. 3,372,871 in which vapor generated in the boiler is utilized to force the liquid through the conduit and into the heat exchanger and then is condensed to create a partial vacuum for drawing the liquid back into the boiler for reheating and for circulation through another cycle. The above-described patented system operates intermittently in that the supply of heat to the boiler is cut off during the time the vapor is being condensed.

SUMMARY OF THE INVENTION The primary aim of the present invention is to provide a new and improved single pipe heating system of the above general character which is capable of circulating the liquid more rapidly through repeated cycles than previous systems so that a greater quantity of heated liquid will be circulated through the heat exchanger in a given time interval to produce a more uniform heating effect.

A related object of the invention is to effect more rapid cycling'in the system by condensing the vapor in the boiler even while heat is being supplied continuously to the boiler.

Still another object is to simplify the control apparatus for the system and, at the same time, to increase the efficiency of the system by doing away with the need of 3,520,474 Patented July 14, 1970 periodically cutting off the supply of heat to the boiler to elfect condensation of the vapor.

Another object is to retain hot liquid in the boiler for a longer period of time than has been accomplished heretofore in order to increase the temperature of the liquid flowing from the boiler and to lengthen the time interval during which hot liquid flows through the heat exchanger.

The invention also resides in the provision of a novel accumulator tank for storing relatively cool liquid and in the unique manner of dumping the cool liquid into the boiler to effect condensation of the vapor therein.

Other objects and advantages of the invention will become apparent from the following detailed description when taken in conjunction with the accompanying draw- 1ngs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic elevational view of one embodiment of a new and improved heating system incorporating the novel features of the present invention, the system being shown in a shut down condition prior to the application of heat to the boiler.

FIG. 2 is a view similar to FIG. 1 but showing the system as the hot liquid is being forced from the boiler.

FIG. 3 is a view similar to FIG. 1 but showing the system as the relatively cool liquid is being dumped into the boiler to condense the vapor.

FIG. 4 is a view similar to FIG. 1 but showing the system as the liquid starts returning to the boiler.

FIG. 5 is a view similar to FIG. 1 but showing the system as the boiler is refilled with the returning liquid.

FIG. 6 is a view similar to FIG. 1 but showing a second embodiment of a heating system incorporating the features of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the drawings for purposes of illustration, the invention is embodied in a space heating system which is particularly suitable for use in warming small enclosed areas such as travel trailers and the like. In such a system, water, propylene glycol or other suitable liquid 10 is heated in a chamber defined by a boiler 11 and is circulated through one or more heat exchangers or radiators 12 within the enclosed area thereby losing a portion of its heat to the air surrounding the radiators. The cooled liquid then is returned to the boiler for reheating, and the cycle is repeated until the area has been warmed to the desired temperature.

Herein, the exemplary boiler 11 includes a walled combustion chamber formed by a tube 13 disposed within the boiler chamber and surrounded by the liquid 10 to be heated. The boiler is flame fired by gas or liquid fuel which flows from an inlet 14 into a heating mechanism or burner 15, and then into the combustion tube. When the area has been heated in accordance with the setting of a room thermostat 17, a bi-metallic element 18 housed within the thermostat opens a switch contact 19 to deenergize a solenoid 20. De-energization of the solenoid causes a valve 21 in the inlet 14 to close thereby shutting off the flow of fuel to the burner. When the thermostat again calls for heat, the bi-metallic element makes contact 19 to energize the solenoid and to open the valve thus permitting fuel to flow to the burner.

Similar to the heating system disclosed in the abovementioned patent, the present system avoids the need for electrically operated pumps or gravitational force for circulating the liquid through the radiators 12, and also both feeds the liquid to the radiators and returns the liquid to the boiler 11 through a single conduit 22. As shown, the conduit leads from the lower portion of the boiler to the radiators and then leads to a reservoir 23. As heat is supplied to the combustion tube 13, the liquid is heated, and vapor is generated in the upper portion of the boiler chamber, the volume and pressure of the vapor increasing as additional heat is supplied. This increase in vapor pressure forces the hot liquid downwardly through the conduit 22, into the radiators 12, and then into the storage tank 23. To return the liquid in the opposite direction through the conduit and back to the boiler, the vapor in the boiler is cooled and condensed to create a partial vacuum within the boiler chamber. The vacuum acts to draw the liquid in a reverse direction (FIG. 4) through the conduit from the reservoir, through the radiators, and then back into the boiler.

According to the primary aspect of the present invention, the vapor in the boiler 11 is condensed by supply of relatively cool liquid 24 which is dumped periodically into the boiler when the liquid 10 therein falls to a predetermined level as a result of being forced through the radiators 12. The cooler liquid 24 entering the boiler causes the vapor to condense and form a vacuum for drawing the circulating liquid 10 back into the boiler even though heat is supplied continuously to the boiler by the burner 15. With this arrangement, there is no need of cutting off the supply of heat to the boiler to condense the vapor and, as a result, the system is capable of recycling almost immediately to force another charge of hot liquid through the radiators and thereby keep the radiated heat within a more uniform range of temperatures. Since the burner fires the boiler continuously during the entire interval that the thermostat 17 calls for heat, the efficiency of the system is not reduced as otherwise would result from intermittent shutting down and re-firing of the burner within the interval and, in addition, standard control apparatus may be used for governing the system.

In the present instance, the supply of relatively cool liquid 24 is stored in a container in the form of an accumulator tank 25 which is located outside of and above the boiler 11 so that the liquid 24 is heated to a much lesser degree than the liquid 10 when the boiler is fired. Extending between and communicating with the tank and the boiler is an open vapor pipe 26 whose upper end is located near the top of the tank and whose lower end normally is immersed in the liquid 10 in the boiler. An outlet pipe 27 also extends between the tank and the boiler but is located with its upper end disposed near the bottom of the tank. The lower end of the outlet pipe normally is closed by a valve 29 which includes a floating member in the form of a ball 30 adapted to be forced upwardly into closing relation with the pipe when the liquid in the boiler is at or above a predetermined level.

Initially, the tank 25, the boiler 11 and the conduit 22 are completely fillled with liquid, a relatively small quantity of liquid is stored in the reservoir 23, and the valve 29 is closed with respect to the outlet pipe 27 (see FIG. 1). When the thermostat 17 calls for heat, the burner 15 fires the boiler to heat the liquid 10 and to build up the vapor pressure within the boiler. The liquid 10 thus is forced out of the lower portion of the boiler and into the conduit 22 and the flows through the radiators 12 and into the reservoir as shown in FIG. 2. When the level of the liquid in the boiler drops below the lower end of the vapor pipe 26 (see FIG. 3), the liquid in and above that pipe falls into the boiler chamber thereby allowing vapor to rise to the top of the tank 25. The admission of vapor into the tank breaks the siphon effect and substantially balances the pressure on opposite sides of the floating ball 30 such that the weight of the liquid 24.in the tank is effective to force the ball downwardly to open the valve 29. With the valve open, the entire supply of relatively cool liquid 24 in the tank is dumped through the outlet pipe 27 to cool and condense the vapor in the boiler. The tank 25 is of such volume that the cooling capacity of the liquid 24 is significantly greater than the rate at which heat is applied to the liquid 10 by the burner 15. As a result, the vapor in the boiler condenses in spite of the fact that the burner remains activated and continues to heat the liquid 10 during the time such condensation occurs.

The vacuum resulting from the vapor condensing within the boiler 11 draws the liquid out of the reservoir 23 and reversely through the radiators 12 and the conduit 22 (see FIG. 4). After passing through the radiators, the returning liquid is drawn into a return line 31 which is connected at one of its ends to the tank 25 and at the other of its ends to the conduit 22 at a location between the boiler and the first radiator 12. The returning liquid flowing through the return line 31 thus is directed into the tank and flows into the boiler 11 through the outlet pipe 27 and the open valve 29. Advantageously, a one-way valve 33 is incorporated in the conduit 22 be tween the boiler and the return line 31 to prevent the returning liquid from flowing directly into the lower part of the boiler while still permitting hot liquid to flow into the radiators 12 during the heating portion of the cycle. Also, the return line 31 is equipped with a one-way valve 34 which permits the returning liquid to flow into the tank 25 but which prevents the liquid from flowing out of the tank when the latter is filled.

As the returning liquid spills into the boiler 11 through the outlet pipe 27, the liquid level in the boiler rises as shown in FIG. 5. When the liquid reaches a predetermined level, the floating ball 29 rises and closes the outlet pipe so that the remaining liquid returning through the line 31 refills the tank 25 for another operating cycle. Being filled with the last of the liquid returning from the reservoir 23, the tank contains the coldest liquid available in the system and uses such liquid for subsequently condensing the vapor during the next cycle.

During the time the tank 25 is being refilled with the returning liquid, the vapor pressure again builds up in the boiler 11 to force another charge of hot liquid through the radiators 12. Thus, the system cycles substantially continuously without any interruption of the supply of heat to the boiler so that the elapsed time between the forcing of successive charges of hot liquid into the radiators is kept comparatively short to promote more uniform heating of the space surrounding the radiators. The burner 15 shuts down only when the room thermostat 17 is satisfied and thus the efliciency of the system is relatively high since the burner need not be de-activated during the time required for condensation of the vapor and then re-activated to heat the liquid after the latter has returned to the boiler. In addition, no specialized apparatus is required to control the heating mechanism.

It will be apparent that the novel coaction existing between the vapor pipe 26, the outlet pipe 27 and the valve 29 enables the latter to open when the liquid 10 is at one level in th boiler 11 and to close when the liquid is at a higher level. This allows the boiler to be filled almost completely with the returning liquid and yet delays the dumping of the cooler liquid 24 into the boiler until the liquid 10 therein has fallen to a relatively low level and a predetermined quantity of liquid has been forced through the radiators.

In some applications, the reservoir23 is closed to the atmosphere (i.e., unvented) in order to extend the time interval during which high temperature liquid flows through the radiators 12. Air or gas trapped above the liquid in the sealed reservoir is compressed against the top of the reservoir by the inflowing liquid and acts to retard the flow of liquid from the boiler 11 to cause the vapor pressure and boiling point of the liquid in the boiler to rise gradually. The compressed air builds up a pressure within the system to change the vapor pressure of the liquid in proportion to the absolute value of the air pressure. The length of time required to empty the boiler thus is extended to avoid periods of non-uniform heating and, in addition, a greater amount of heat is transferred to the radiators since the temperature of the liquid flowing from the boiler is higher. Also, the compressed air acts as a piston and assists in returning the liquid reversely through the conduit 22 when the vacuum is created in the boiler. The volume of the reservoir may be varied to allow operation of the system at any desired temperature.

Instead of using the sealed reservoir 23, the foregoing advantages may be achieved with a relatively tall reservoir 23' (FIG. 6) which is open at its top and exposed to the atmosphere. The liquid column in the reservoir 23' increases in height in direct proportion to the amount of liquid forced from the boiler 11, and exerts a retarding force causing a rise in the vapor pressure and boiling point of the liquid from the boiler. The geometry of the reservoir 23 may be varied to change the temperature at which the liquid flows from the boiler.

We claim as our invention:

1. A heating system having a boiler with a chamber within which to heat liquid, a heat exchanger for transferring heat from the liquid thereby to cool the liquid, a reservoir for storing the cooled liquid, a conduit leading from the lower portion of said chamber to said heat exchanger and then to said reservoir, and heating mechanism associated with said boiler and operable to heat the liquid in said chamber and to increase the pressure of the vapor therein whereby the pressure exerted on the heated liquid by the vapor forces such liquid in one direc tion through said conduit from said chamber to said heat exchanger and then to said reservoir and causes the level of the liquid in the chamber to drop, the improvement in said system comprising, a container for storing a supply of liquid and capable of keeping such liquid colder than that in the chamber when said heating mechanism is operating, said container communicating with said chamber and being responsive to the liquid therein dropping below a predetermined level to introduce said colder liquid into said chamber thereby to cool and condense the vapor in the chamber and to create a partial vacuum in the chamber for returning the liquid in the opposite direction through said conduit from said reservoir to said chamber, and said container communicating with said conduit and arranged to be refilled with liquid returning through the conduit.

2. A heating system having a boiler with a chamber within which to heat liquid, a heat exchanger for transferring heat from the liquid thereby to cool the liquid, a reservoir for storing the cooled liquid, a conduit leading from the lower portion of said chamber to said heat exchanger and then to said reservoir, and heating mechanism associated with said boiler and operable to heat the liquid in said chamber and to increase the pressure of the vapor therein whereby the pressure exerted on the heated liquid by the vapor forces such liquid in one direction through said conduit from said chamber to said heat exchanger and then to said reservoir and causes the liquid in said chamber to drop from an upper level to a lower level, the improvement in said system comprising, a tank located above said chamber for holding a supply of liquid colder than that in said chamber, a pipe establishing communication between said tank and said chamber, a valve normally closing said pipe and operable to open the pipe in response to the liquid in the chamber falling to said lower level thereby to dump the cold liquid in the tank into said chamber to cool and condense the vapor in the chamber and create a partial vacuum therein for returning the liquid in the opposite direction through said conduit from said reservoir, a return line communicating at one end with said conduit and communicating at its opposite end with said tank to direct the returning liquid into the tank from where such liquid is directed back into said chamber through said pipe, and said valve being operable to close said pipe in response to the returning liquid filling said tank to said upper level whereby the remaining returning liquid refills the tank for the next operating cycle.

3. A heating system as defined in claim 2 in which said reservoir is closed to the atmosphere whereby gas within the reservoir is compressed by the liquid flowing through said conduit and retards the flow of liquid in said one direction while assisting the flow of liquid in the opposite direction.

4. A heating system having a boiler with a chamber within which to heat liquid, a heat exchanger for transferring heat from the liquid thereby to cool the liquid, a reservoir for storing the cooled liquid, a conduit leading from the lower portion of said chamber to said heat exchanger and then to said reservoir, and heating mechanism associated with said boiler and operable to heat the liquid in said chamber and to increase the pressure of the vapor therein whereby the pressure exerted on the heated liquid by the vapor forces such liquid in one direction through said conduit from the lower portion of said chamber to said heat exchanger and then to said reservoir and causes the liquid in the chamber to drop from an upper level to a lower level, the improvement in said system comprising, a tank located above and outside of said chamber for holding a supply of liquid colder than that in the chamber, a vapor pipe communicating between said chamber and said tank and having an open upper end located near the top of said tank, said vapor pipe having a lower end immersed in the liquid in the chamber when such liquid is at said upper level and located above the liquid in the chamber when such liquid is at said lower level whereby vapor in the chamber is admitted into said tank through said vapor pipe when said liquid in said chamber drops to said lower level, an outlet pipe communicating between said chamber and said tank and having an open upper end disposed below the level of the liquid in said tank and having an open lower end disposed higher than said lower level, a valve normally closing said outlet pipe and operable to open the latter in response to the admission of vapor into said tank through said vapor pipe whereby, when the liquid in said chamber drops to said lower level, the cold liquid 1n said tank is dumped into said chamber through said outlet pipe and cools and condenses the vapor in the chamber to create a partial vacuum therein for returning the liquid in the opposite direction through said conduit from said reservoir, a return line communicating at one end with said conduit between said heat exchanger and said chamber and communicating at its other end with said tank to direct the returning liquid into the tank whereby such liquid may flow back into said chamber through said outlet pipe, and said valve being operable to close said outlet pipe in response to the returning liquid filling the chamber to said upper level whereby the remaining returning liquid refills the tank for the next operating cycle.

5. A heating system as defined in claim 4 further including a one-way valve located in said conduit between said chamber and said return line and operable to permit liquid to flow from said chamber through said conduit in said one direction while restricting the flow of liquid from said conduit directly into the chamber in the opposite direction thereby to cause the returning liquid to flow back into the chamber by way of said return line and said tank.

6. A heating system as defined in claim 5 further including a one-way valve located in said return line and 7 operable to restrict the flow of liquid from said tank into said return line while permitting the returning liquid to flow from said line into said tank.

7. A heating system as defined in claim 4 in which said valve includes a member supported to move into a closed position with respect to said outlet pipe in response to the liquid in said chamber reaching said upper level, said member being held in said closed position when the liquid in the chamber is between said upper level and said lower level, and said member being forced to an open position with respect to said outlet pipe by the weight of the liquid in said tank when the liquid in the chamber drops to said lower level to admit vapor into the tank through said vapor pipe.

References Cited UNITED STATES PATENTS 1,581,591 4/1926 Moreau 23764 1,629,043 5/ 1927 Moreau 23764 3,372,871 3/1968 Pfluger 237-64 X EDWARD '1. MICHAEL, Primary Examiner 

